The present invention relates to a drill pipe, in particular a drill pipe including a valve assembly for closing a side bore in the drill pipe.
The drilling of a borehole or well is typically carried out using a steel pipe known as a drill pipe or drill string with a drill bit on the lowermost end. The drill string comprises a series of tubular sections, which are connected end to end.
The entire drill string may be rotated using a rotary table, or using an over-ground drilling motor mounted on top of the drill pipe, typically known as a ‘top-drive’, or the drill bit may be rotated independently of the drill string using a fluid powered motor or motors mounted in the drill string just above the drill bit. As drilling progresses, a flow of mud is used to carry the debris created by the drilling process out of the borehole. Mud is pumped down the drill string to pass through the drill bit, and returns to the surface via the annular space between the outer diameter of the drill string and the borehole (generally referred to as the annulus). The mud flow also serves to cool the drill bit, and to pressurise the borehole, thus substantially preventing inflow of fluids from formations penetrated by the drill string from entering into the borehole. Mud is a very broad drilling term and in this context it is used to describe any fluid or fluid mixture used during drilling and covers a broad spectrum from air, nitrogen, misted fluids in air or nitrogen, foamed fluids with air or nitrogen, aerated or nitrified fluids to heavily weighted mixtures of oil and or water with solid particles.
Significant pressure is required to drive the mud along this flow path, and to achieve this, the mud is typically pumped into the drill string using one or more positive displacement pumps which are connected to the top of the drill string via a pipe and manifold.
Whilst the main mud flow into the well bore is achieved by pumping mud into the main bore at the very top end of the drill string, it is also known to provide the drill string with a side bore which extends into the main bore from a port provided in the side of the drill string, so that mud can be pumped into the main bore at an alternative location to the top of the drill string.
For example, as drilling progresses, and the bore hole becomes deeper and deeper, it is necessary to increase the length of the drill string, and this is typically achieved by disengaging the top drive from the top of the drill string, adding a new section of tubing to the drill string, engaging the top drive with the free end of the new tubing section, and then recommencing drilling. It will, therefore, be appreciated that pumping of mud down the drill string ceases during this process.
Stopping mud flow in the middle of the drilling process is problematic for a number of reasons, and it has been proposed to facilitate continuous pumping of mud through the drill string by the provision of a side bore in each section of drill string. This means that mud can be pumped into the drill string via the side bore whilst the top of the drill string is closed, the top drive disconnected and the new section of drill string being connected.
In one such system, disclosed in U.S. Pat. No. 2,158,356, at the top of each section of drill string, there is provided a side bore which is closed using a plug, and a valve member which is pivotable between a first position in which the side bore is closed whilst the main bore of the drill string is open, and a second position in which the side bore is open whilst the main bore is closed. During drilling, the valve is retained in the first position, but when it is time to increase the length of the drill string, the plug is removed from the side bore, and a hose, which extends from the pump, connected to the side bore, and a valve in the hose opened so that pumping of mud into the drill string via the side bore commences. A valve in the main hose from the pump to the top of the drill string is then closed, and the pressure of the mud at the side bore causes the valve member to move from the first position to the second position, and hence to close the main bore of the drill string.
The main hose is then disconnected, the new section of tubing mounted on the drill string, and the main hose connected to the top of the new section. The valve in the main hose is opened so that pumping of mud into the top of the drill string is recommenced, and the valve in the hose to the side bore closed. The resulting pressure of mud entering the top of the drill string causes the valve member to return to its first position, which allows the hose to be removed from the side bore, without substantial leakage of mud from the drill string.
The side bore may then be sealed permanently, for example by welding a plug onto the side bore, before this section of drill string is lowered into the well.
The drill string may also be provided with a side bore in what is known as a “pump in sub”, which is used in the event of an emergency, for example to facilitate the provision of additional mud pressure required to control a sudden surge in well-bore pressure due to fluid inflow from a formation penetrated by the well entering the well in what is known as a “kick”.